Transcript

1.
Bedajangam SagarKishor et al Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 4, Issue 2( Version 6), February 2014, pp.33-36
RESEARCH ARTICLE
OPEN ACCESS
Optimization of Geometrical Parameters of Four Stroke Engine
Piston
BedajangamsagarKishora, N. P. Jadhavb
a
Mechanical Department, SAOE, Kondhwa, India
Mechanical Department, SAOE, Kondhwa, India
b
Abstract
The impact of crown thickness, thickness ofbarrel and piston top land height on stress distribution and total
deformation is monitored during the study of actual four stroke engine piston. The entire optimization is carried
out based on statistical analysis. It has been notified that after reducing the geometrical parameters of piston the
stress distribution and total deformation is increased which is within the desirable tolerance limit. FEA analysis
is carried out using ANSYS for optimum geometry. The work describes the mesh optimization with using finite
element analysis technique to predict the higher stress and critical region on the component.
Key words: FEA, Crown thickness, Thickness ofbarrel, Top land height, Statistical analysis.
I.
Introduction
A piston is a component of reciprocating ICengines. It is the moving component that is contained
by a cylinder and is made gas-tight by piston rings. In
an engine, its purpose is to transfer force from
expanding gas in the cylinder to the crankshaft via a
piston rod and/or connecting rod. As an important
part in an engine, piston endures the cyclic gas
pressure and the inertial forces at work, and this
working condition may cause the fatigue damage of
piston, such as piston side wear, piston head/crown
cracks and so on. The investigations indicate that the
greatest stress appears on the upper end of the piston
and stress concentration is one of the mainly reason
for fatigue failure.
The two main requirements of the piston are as
follows:
I.
It should contain all the fluids above and
below the piston assembly during the cycle.
II.
It should transfer the work done during
combustion process to the connecting rod
with
minimal
mechanical
and
thermodynamic losses.
The piston is the heart of the internal combustion
engine and is subjected to loads such as thermal and
structural stress. The piston reciprocates within the
cylinder.
Finite Element analysis is a simulation technique
which evaluates the behavior of components,
equipment and structures for various loading
condition including applied forces, pressure and
temperatures. Thus, a complex engineering problem
with nonstandard shape and geometry can be solved
using finite element analysis where a closed form
solution is not available. The finite element analysis
methods result in the stress distribution,
displacements and reaction loads at supports for the
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model. FEA techniques can be used for mesh
optimization, design optimization, material weight
reduction, and shape optimization.
II.
Geometric modeling
ANSYS module Design Modeler was used
togenerate (Figure 2.1) and to parameterize (Figure
2.2)geometric model of piston. To avoid
regenerationfailures mathematical relations were
created betweenparameters and other dimensions by
means of theDesign Modeler parameter manager.
Figure 2.1: Geometry of Piston in Ansys.
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Bedajangam SagarKishor et al Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 4, Issue 2( Version 6), February 2014, pp.33-36
Figure 2.2: Parameterizegeometric model of
Piston
III.
Material properties and boundary
conditions
Piston material was assumed to be
aluminum alloy which is homogenous,isotropic and
linear elastic with a Poisson’s ratio of 0.33 and a
young's modulus of 71GPa [2]. The model is loaded
with a gasforce on the piston head (piston crown)
(Figure 3.2). Fixed support is at the pin bore(Figure
3.1).
Table 1: Material Properties of Al
Density (Kg/m3)
Tensile ultimate strength (Pa)
Tensile Yield strength (Pa)
Compressive Yield strength (Pa)
2770
3.10E+08
2.80E+08
2.80E+08
Figure 3.1: Frictional Less fixed support
(Boundary Condition 1)
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Figure 3.2: Downward gas force acting of
Piston crown (Boundary Condition 2)
IV.
Meshing
The meshing strategy for the optimization is
not exactlythe same as for a single finite element
analysis. Themesh for the optimization task has to
meet four differentrequirements:
 Automated meshing must be possible for
changing edges, angles and surfaces;
 The mesh quality must be comparable for
every parameter combination;
 Accurate results for the changing geometry;
 In light of the expected number of
calculations the calculation time should not
be too long.
For a single finite element analysis it would be
possibleto locate problematic regions with high stress
gradientsand to refine the mesh at these specific
regions. Butconcerning the second requirement this is
not possiblefor the optimization model because
critical regions aswell as maximal stress can change
the location due toparameter variation. At this point
sensitivity analysiswas started to unveil some
important features of thefinite element model: are
there any regenerationproblems, can the ANSYS
Workbench mesher alwaysfind a mesh, where are the
maximal stresses located.With ANSYS module
Simulation moderate changes inthe geometry within
the variation range of parameterswere made, many
meshes with different element sizewere generated
and finite element analyses were madefor many
models with different geometry and differentmesh.
Results of these analyses were used to comparenodal
solution with element solution to get an idea ofresult
quality. At the end the final mesh with thefollowing
characteristics was generated: a generalelement size
for the model was 4 mm, the relevance forthe model
was set to 100 that is the highest level and theshape
checking mode was set to aggressive. The finalmodel
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3.
Bedajangam SagarKishor et al Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 4, Issue 2( Version 6), February 2014, pp.33-36
was
meshed
with
17636
nonlinear
tetrahedralelements with 9431 nodes (Figure 4.1).
Figure 6.1: Total deformation before optimization
Figure4.1: Meshing Model of Piston.
V.
Optimization Analysis of Aluminum
Alloy Piston
To study the influence of parameters on
piston stress levels, number of iteration are run using
optimization tool in Ansys. Through these results it
was possible to choose the best value for each
parameter taking into account the stress levels on the
piston and the mass of the piston. The aim is to
obtain an assembly as light as possible and with some
safety margin.
Factor of safety = Yield point stress / Working or
Design Stress.
Automobile industries use factor of safety between
2.0 to 3.0 [7]. As piston is a critical component we
are considering Factor of safety as 2.25. For
Aluminum alloy, tensile strength is 280 MPa, Tensile
Ultimate strength is 310 MPa. And mass of piston is
0.10194 Kg.
Working or design stress = 280 / 2.5 =124 MPa.
Based on above analysis the maximum stress induce
in the 67 MPa, which is less than 124 MPa (allowable
stress). Hence piston safe and there is a scope for
optimization.
So from the optimization results it is clear that the
dimension 5.0mm can be reduced to 4.10mm,
dimension 7.0mm can be reduce to 6.0mm,
dimension 3.7mm can be reduce to 3.6mm. This
result in Max equivalent stress of 105.12 MPa which
is less than 124 MPa and solid mass is reduced to
0.09498 Kg. So from these result, piston model is
modified to new dimensions and static analysis is
carried out. The results obtained are well below the
working stress and mass of piston is also reduced.
VI.
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Figure 6.2: Total deformation after optimization
Figure 6.4: Equivalent stress before optimization.
Results and Discussion
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Bedajangam SagarKishor et al Int. Journal of Engineering Research and Applications www.ijera.com
ISSN : 2248-9622, Vol. 4, Issue 2( Version 6), February 2014, pp.33-36
References
Figure6.3: Equivalent stress after optimization.
In this paper work analysis is done on actual piston
which is used in 150cc engine. The result shows that
the parameter crown thickness is mainly affecting on
change in stress acting at piston head. The optimize
result are shown in Table 6.1 below;
Table 6.1 Optimization Result
Before
Optimization
After
Optimization
5
4.10
7
6
67.01
105.12
0.05537
0.09884
1.0158
0.94643
36803
Parameters
[1] Mi Yan, Wang Tao," Finite Element
Analysis of Cylinder Piston Impact Based on
ANSYS/LS-DYNA", MEMS 2012.
[2] Ch.VenkataRajam,
P.V.K.Murthy,
M.V.S.Murali Krishna, G.M.PrasadaRao,
“Design Analysis and Optimization of Piston
using CATIA and ANSYS", January 2013,
issue 2 volume 1.
[3] Anil
kumar,
Kamaldeep
Grover,
BalvinderBudania,"
Optimization
of
Connecting Rod Parameters using CAE
Tools", Vol. 1 Issue 3 September 2012.
[4] Thet
T.
Mon,
RizalmanMamat,
NazriKamsah, "Thermal Analysis of SIEngine using Simplified Finite Element
Model",Vol III WCE 2011, July 6 - 8, 2011.
[5] Ghodake A. P., Patil K.N, “Piston Design
and Analysis by CAE Tools ", ISSN: 22503021 ISBN: 2878-8719 PP 33-36 National
Symposium on engineering and Research.
[6] Pravardhan S. Shenoy and Ali Fatemi,
"Connecting Rod Optimization for Weight and
Cost Reduction", 2005-01-0987.
34291
Thickness of
crown (mm)
Thickness of
barrel (mm)
Equivalent
stress (MPa)
Total
Deformation
(mm)
Mass of piston
(Kg)
Volume of
Piston (mm3)
VII.
Conclusion
The FEA is carried out for actual piston
which is used in 150cc four stroke petrol engine and
results of analysis indicate that the stress and total
deformation are increase in same rate.
 The stress is increase within the allowable
limit i.e. below 124 MPa.
 The thickness of piston crown is optimizing
at 16% because of this stress is increase at
36.25% and deformation increase at 44%.
 In this optimization found that mass is
reduced at 7%.
 From optimization results it is clear that
there is a scope for reduction in the
thickness of piston skirt, piston crown wall
thickness and piston crown thickness.
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